1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copying machine, a printer, a facsimile, and an MFP (multifunction printer), and in particular to an image forming apparatus having a duplex recording function.
2. Description of Related Art
There have conventionally been proposed various constructions where duplex recording functions are given to image forming apparatuses, such as a copying machine, a printer, and a facsimile. A conventional image forming apparatus will be described by taking a facsimile as an example. FIG. 7 is an overall construction diagram of a facsimile having a duplex recording function according to a conventional technique.
In FIG. 7, the front of the main body of apparatus 100 is rightward in FIG. 7 (in th direction indicated by the arrow A). An image reading portion 300 is provided in the upper part of the apparatus, an image forming portion 101 is provided in the approximately center part thereof, and a sheet feeding portion 110 is provided in the lower part thereof. Also, duplex recording unit 200 including surface reversing means and a re-feed and transporting path is provided between the image forming portion 101 and the sheet feeding portion 110. Further, on the upper surface of the apparatus, there is arranged an operation portion 130 that includes buttons and a display portion that are not shown in FIG. 7.
In the image reading portion 300, an original S stacked on an original stacking tray 301 is fed by a separation roller pair 302. After image information is read by a contact-type image sensor 303, the original S is delivered to an original delivery tray 304. The read image information is transmitted by a communication means (not shown) or is sent to the image forming portion 101, which then records the image information on a sheet.
The image forming portion 101 has a process cartridge 102 that is constructed by integrating a photosensitive drum 103 that is an image bearing member, a charging means 104, a developing means 105, and a cleaning means 106. Also, an optical means 107 is arranged above the process cartridge 102. The optical means 107 irradiates a laser beam onto the photosensitive drum 103, which has been uniformly charged by the charging means 104, according to the image information. In this manner, an electrostatic latent image is formed. The electrostatic latent image is visualized by the developing means 105, thereby forming a toner image. After the toner image is transferred to a fed sheet by a transferring means 108, residual toner on the photosensitive drum 103 is removed by the cleaning means 106.
A sheet is fed from the sheet feeding portion 110 provided in the lower part of the apparatus or from a multi-feeding portion 115 provided in a side part of the apparatus. The sheet feeding portion 110 is capable of stacking and storing sheets on a feeding tray 111 and the sheets are separated and fed by a feeding roller 112 and a separation roller pair 113 one by one. In this manner, each sheet is fed to a registration roller pair 114 on the upstream side of the image forming portion 101. As to the multi-feeding portion 115, sheets are inserted by opening a multi-tray 116 and are fed to the registration roller pair 114 by a multi-separation portion 117.
The registration roller pair 114 transports each sheet in synchronism with the toner image on the photosensitive drum 103. After the toner image is transferred to the sheet by a nip between the photosensitive drum 103 and the transferring means 108, a transporting means 118 transports the sheet to a fixing means 119, which then applies heat and pressure to the sheet. In this manner, the toner image is permanently fixed. The transporting path of the sheet, on which the toner image has been fixed, is switched by a flapper 120. If the image formation is to be finished, the sheet is delivered to the outside of the apparatus. If an image is to be recorded on the second side, the sheet is re-fed to the image forming portion 101 by the duplex recording unit 200.
If the image formation is to be finished, the sheet is delivered to any one of two delivery trays 122 and 123 so that the recording surface faces down (face-down delivery). The delivery trays 122 and 123 are provided between the image forming portion 101 and the image reading portion 300. The selection between the delivery trays 122 and 123 is performed by a flapper 121 according to the control performed for the sheet to be delivered.
If an image is to be recorded on the second side, the sheet is guided by the flapper 120 to the duplex recording unit 200 connected to a back delivery portion 124. The sheet is delivered from the back delivery portion 124 so that the recording surface faces up (face-up delivery), and is transported by a surface reversing roller pair 202 from a duplex transporting path 201 to a surface reverse path 203. Following this, when the trailing edge of the sheet reaches the vicinity of the surface reversing roller pair 202, the transport direction is reversed and the sheet is transported to a re-feed and transporting path 204, with the trailing edge being transported thereto first. Then, the sheet is further transported by a transporting roller pair 205 to a feeding roller pair 109 on the main body side. After an image is recorded on the second side in the same manner as above, the sheet is delivered to the delivery tray 122 or 123.
Here, the duplex recording unit 200 is mountable to and detachable from the main body of the apparatus (in the direction indicated by the double-headed arrow K), which makes it possible for a user to pull out the duplex recording unit 200 to remove a jamming sheet or the like from the duplex recording unit 200.
To perform duplex recording in the manner described above, it is required to reverse a sheet delivered from the main body of the apparatus. Therefore, the surface reverse path 203 having a U-turn shape is formed with the aforementioned conventional construction, which means that the duplex recording unit 200 significantly projects backward from the apparatus. Accordingly, the size of the apparatus is increased by the amount of this projection B. This results in problems that a production cost is increased and an installation space is also increased.
Also, the surface reverse path 203 and the re-feed and transporting path 204 are formed below the image forming portion 101, so that the overall height of the apparatus is also increased by the height C required to form these paths. This increase of the apparatus height results in the increase of a size of the apparatus, which in turn increases a production cost. The increase of the apparatus height also increases the heights of the original stacking tray 301, the original delivery tray 304, the delivery trays 122 and 123, an operation panel of the operation portion 130, and the like. Accordingly, this problem particularly becomes serious in the case of a desktop-type apparatus that is used on a desk.
Meanwhile, as a means for reducing the size of the apparatus, there may be reduced the radius of the U-turn portion; through which a sheet passes when it is fed from the re-feed and transporting path 204 to the feeding roller pair 109 on the apparatus main body side, or there may be reduced the radius of the U-turn portion of the surface reverse path 203. However, if the radius of such U-turn portions are reduced, this increases the resistance that occurs during the transport of a sheet. As a result, there are various adverse effects. For instance, jams tend to occur, particularly when thick sheets are used. Also, the reliability of sheet transportation is reduced and the sheets that are usable are limited to thin sheets.
In view of these problems, the object of the present invention is to provide a desktop-type image forming apparatus having a duplex recording function, in which the increase of a size of the apparatus is avoided, the operability of an operation portion and a reading portion is improved, an installation space is saved, high reliability is realized, and a jam clearance property is improved.
In order to solve the above-mentioned problems, an image forming apparatus according to the present invention has an exemplary structure, which includes: a sheet feeding portion arranged in a back part of a main body of the apparatus; an image forming portion arranged in an approximately center part of the main body of the apparatus; a sheet delivery portion arranged in a front part of the main body of the apparatus; one of an operation portion and an image reading portion arranged in a front upper part of the main body of the apparatus; a surface reversing means for reversing a transport direction of a sheet on which an image has been recorded; and a re-feed and transporting path for guiding the reversed sheet to the image forming portion, in which the surface reversing means is arranged below one of the operation portion and the image reading portion, and the re-feed and transporting path is arranged between the sheet feeding portion and one of the operation portion and the image reading portion as well as above the image forming portion.